Traceroute works by sending ICMP packets to test each hop along the route. It will send out three packets, and then increase the time to live (TTL) setting by one each time. This effectively allows the packets to go one hop farther along the route. This is the reason why most traceroute commands display their maximum hop count before they start tracing the route — that is the maximum number of steps it will take before declaring the destination unreachable. Also the TTL setting may result in steps along the route timing out due to slow responses. There are many possible reasons for this to occur.

Traceroute by default uses UDP datagrams with destination ports numbered from 33434 to 33534. The traceroute utility usually has an option to specify use of ICMP echo request (type 8) instead, as used by the Windows tracert utility. If you have a firewall and if you want traceroute to work from both machines (Unix-like systems and Windows) you will need to allow both protocols inbound through your FortiGate security policies (UDP with ports from 33434 to 33534 and ICMP type 8).